Qualified Employee Benefit Plans - Amounts Recognized in Other Comprehensive (Loss) Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan, Amounts Recognized in Other Comprehensive Income (Loss) [Abstract]
Prior service cost	$ 93	$ (895)	$ (5,197)
Changes in employee benefit related items	(2,950)	2,372	(24,853)
Employee benefit related items, net of tax	(2,972)	2,207	(24,555)
Retirement Plan [Member]
Defined Benefit Plan, Amounts Recognized in Other Comprehensive Income (Loss) [Abstract]
Unrecognized net (loss) gain from experience different from that assumed and effects of changes and assumptions	(3,115)	2,882	(20,803)
Prior service cost	93	(895)	0
Changes in employee benefit related items	(3,022)	1,987	(20,803)
Income tax (expense) benefit	(10)	(99)	232
Employee benefit related items, net of tax	$ (3,032)	$ 1,888	$ (20,571)